BuddyPress.org

Reading your post, I think the answer is “hire a theme developer to make it look right.”

First of all, you need to get a test server (even if it’s locally on your machine) setup with a base WordPress install with your theme and then install BuddyPress and then this.

There will be changes which you’ll need to adapt to, but the above-linked BP Template Pack plugin should get you started (or at least let you assess whether the changes are something you can do or whether it’s something you need to hire a developer for).